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Some of the text in this readme has been copied directly from the book and all the respective credit goes to the authors of the original text.

INTRODUCTION:

The SIMPLETRON contains an accumulator — a "special register" in which information is put before the SIMPLETRON uses that information in calculations or examines it in various ways. All information in the SIMPLETRON is handled in terms of words. A word is a signed decimal number such as +3364, -1293, +0007, -0001 and so on. The SIMPLETRON is equipped with a 100-word memory (in its default configuration, but this can be varied by changing the macro "MEM_SIZE" in "SIMPLETRON.h") and these words are referenced by their location numbers 00, 01, ..., 99.

Before running an SML (SIMPLETRON Machine Language) program, we must load or place the program into memory. The first instruction (or statement) of every SML program is always placed in location 00. Each instruction written in SML occupies one word of the SIMPLETRON’s memory. Each location in the Simpletron’s memory may contain either an instruction, a data value used by a program or an unused (and hence undefined) area of memory. The first two digits of each SML instruction are the operation code, which specifies the operation to be performed. ALL SML operation codes are summarised ahead.

Subsequent digits of each SML instruction are the operand, which is the address of the memory location containing the word to which the operation applies. A dump of all registers and the memory is provided after execution of ALL programs.

The SIMPLETRON is capable of handling floating point numbers.

A description of all the operation codes

  1. Input / Output operatons:

    • 10 Read a word from the terminal into a given location in memory.
    • 11 Write a word from a given location in memory to the terminal.
    • 12 Read a string of characters from the terminal in the given memory location. (Each memory location holds two characters except for the first one which holds one character and the length of the string. Subsequent memory locations are used for the purpose as needed)
    • 13 Write a string of characters to the terminal from a given memory location.
    • 14 Write a newline to the terminal

  2. Load / Store operatons:

    • 20 Load a word from a given location in memory into the accumulator.
    • 21 Store a word from the accumulator into a given location in memory.

  3. Arithmetic operatons:

    • 30 Add a word from a given location in memory to the word in the accumulator (leave result in accumulator).
    • 31 Subtract a word from a given location in memory from the word in the accumulator (leave result in accumulator).
    • 32 Divide a word from a given location in memory into the word in the accumulator (leave result in accumulator).
    • 33 Multiply a word from a given location in memory by the word in the accumulator (leave result in accumulator).
    • 34 Divide what is in the accumulator by a word from a given location in memory and calculate the remainder (leave result in accumulator)
    • 35 Exponentiate what is in the accumulator by a word from a given location in memory (leave result in accumulator)

  4. Transfer-of-control operations:

    • 40 Branch to a specific location in memory unconditionally.
    • 41 Branch to a specific location in memory if the accumulator is negative.
    • 42 Branch to a specific location in memory if the accumulator is zero.
    • 43 Halt - i.e., the program has completed its task and the program execution stops (all memory locations for variables to be reserved AFTER this instruction)

Note: All operands, when needed with a operation code and 00 otherwise, are memory locations.

Sample Program:

This program reads a series of numbers and determines and prints the smallest of them. The first number entered is taken as the number of subsequent inputs.

Memory Location Instruction Comments
00 1021 Read a word from terminal into location 21
01 2021 Load into accumulator the contents of location 21
02 3120 Subtract from accumulator the word in location 20
03 2121 Store from accumulator into location 21
04 1018 Read a word from terminal into location 18)
05 4216 Branch to location 16 if accumulator is zero
06 1019 Read a word from terminal into location 19
07 2018 Load into accumulator the contents of location 18
08 3119 Subtract from accumulator the word in location 19
09 4112 Branch to location 12 if accumulator is negative
10 2019 Load into accumulator the contents of location 19
11 2118 Store from accumulator into location 18
12 2021 Load into accumulator the contents of location 21
13 3120 Subtract from accumulator the word in location 20
14 2121 Store from accumulator into location 21
15 4005 Branch to location 05
16 1118 Write word at location 18 to the terminal
17 4300 HALT instruction for the simpletron
18 0000 variable smaller
19 0000 variable num
20 0001 variable increment
21 0000 variable num_of_loops